Secreção de prostaglandinas antes, durante e após a luteólise em bovinos

• Autor(a) principal: Pugliesi, Guilherme
• Data de Publicação: 2012
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/1800
• topic: Progesterona; Ciclo estral; Progesterone; Estrous cycle; CNPQ::CIENCIAS AGRARIAS::MEDICINA VETERINARIA::REPRODUCAO ANIMAL

The current study was done with the aim to evaluate the role of prostaglandin F2&#945; (PGF2&#945;) synthesis before, during, and afer the luteolytic period on functional and morphological corpus luteum (CL) regression; study the effects of estradiol-17&#946; (E2) in diferrent physiological levels on PGF2&#945; secretion and induction of luteolysis; and evaluate the effects of prostaglandin inhibition during postluteolysis on follicular growth and ovulation in heifers. Four sequential studies were done. The first (Study 1) was elaborated from two experiments, and the other three studies (Studies 2, 3 and 4) were compound by one experiment each. The Study 1 aimed to evaluate the inhibition of the synthesis of prostaglandin F2&#945; (PGF2&#945;) during preluteolytic and luteolytic periods, based on plasma concentrations of a PGF2&#945; metabolite (PGFM). In Experiment 1, flunixin meglumine (FM; 2.5 mg/kg) was given to heifers (n = 4/group) in diferrent doses (0, 0.5, 1.0, or 1.5 g) 16 days after ovulation to evaluate the minimal effective dose during the expected luteolytic period. The dose of 1.5 g (equivalent to 2.5 mg/kg bw) was the most effective. Therefore, in Experiment 2 FM (2.5 mg/kg) was given to heifers at three 8-h intervals, 16 days after ovulation (first treatment = Hour 0). Blood samples were collected at 8-h intervals from 15 to 18 d postovulation in a vehicle (control) and FM group (n = 16/group). Hourly samples were collected from Hours &#8722;2 to 28 in 10 heifers in each group. Heifers that were in preluteolysis or luteolysis at Hour 0 based on plasma progesterone (P4) concentrations at 8-h intervals were partitioned into preluteolytic and luteolytic subgroups. Concentration of PGFM was reduced (P < 0.05) by FM treatment in each subgroup. For the preluteolytic subgroup, the first decrease (P < 0.05) in P4 concentration after Hour 0 occurred at Hours 24 and 40 in the vehicle and FM groups, respectively. Plasma P4 concentrations 32 and 40 h after the beginning of luteolysis in the luteolytic subgroup were greater (P < 0.05) in the FM group. Concentration at the peak of a PGFM pulse in the FM group was greater (P < 0.05) in the luteolytic than in the preluteolytic subgroup. In the second study (Study 2), we aimed to evaluate the effect of E2 concentration on the prominence of PGFM pulses and the relationship between prominence and intrapulse concentration of P4, luinizing hormone (LH), and luteal blood flow were studied. A single dose of 0 (vehicle), 0.01, 0.05, or 0.1 mg of E2 was given (n=6/group) 14 days after ovulation. Blood samples were collected and luteal blood flow was evaluated hourly for 10 h after the treatment. The 0.05-mg dose increased and the 0.1 mg further increased the prominence of the induced PGFM pulse, compared to the 0.0-mg dose and the 0.01-mg dose. The PGFM pulses were subdivided into three different prominence categories (< 50, 50&#8722;150, and > 150 pg/mL at the peak). In the 50 150 category, P4 concentration increased (P < 0.05) between &#8722;2 h and 0 h (0 h = peak of PGFM pulse). In the >150 category, P4 decreased (P < 0.05) between &#8722;1 h and 0 h, LH increased (P < 0.05) at 1 h, and luteal blood flow apparently decreased (P < 0.05) at 2 h of the PGFM pulse. The novel results supported the following hypotheses: 1) an increase in E2 concentration increases the prominence of a PGFM pulse, and 2) greater prominence of a PGFM pulse is associated with a greater transient intrapulse depression of P4 at the peak of the PGFM pulse. In addition, the extent of the effect of PGF2&#945; on the increase in LH and changes in blood flow within the hours of a PGFM pulse was related positively to the prominence of the PGFM pulse. In the subsequent study (Study 3), we aimed to elucidate the effects of sequential induction of PGFM pulses by E2 on prominence of PGFM pulses and P4 concentration. Three treatments of vehicle (n = 12) or E2 (n = 12) at doses of 0.05 mg or 0.1 mg were given at 12-h intervals beginning on day 15 postovulation. Blood samples were collected every 12 h from days 13 to 24 postovulation and hourly for 12 h after the first and third treatments. On day 15, all heifers were in preluteolysis and on day 16 were in preluteolysis in the vehicle-treated heifers (n = 11) and either preluteolysis (n = 4) or luteolysis (n = 8) in the E2-treated heifers. Peak concentration of induced PGFM pulses during preluteolysis on day 15 was greater (P < 0.04) than for pulses during preluteolysis on day 16. The interval from ovulation to the beginning of luteolysis was shorter (P < 0.04) in the E2-treated heifers than in the vehicle-treated heifers. An E2-induced PGFM pulse was less prominent (P < 0.008) in heifers in temporal association with a transient resurgence in P4 than in heifers with a progressive P4 decrease. The hypothesis that repeated E2 exposure stimulates increasing prominence of PGFM pulses was not supported. Instead, repeated exposure reduced the prominence of PGFM pulses in contrast to the stimulation from the first E2 treatment. Results indicated for the first time that reduced prominence of a PGF2&#945; pulse during luteolysis can lead to a transient resurgence in P4 concentration. The Study 4 aimed to study the effects of prostaglandin inhibition during postluteolysis on CL regression, prolactin (PRL) secretion, and follicle growth and ovulation in heifers. The beginning of postluteolysis (P4 < 1 ng/mL) was targeted by using 8 h after ultrasonic detection of a 25% decrease in CL area (cm2) and was designated Hour 0. FM (2.5 mg/kg; n = 10) to inhibit PGF2&#945; secretion or vehicle (n = 9) were given intramuscularly at Hours 0, 4, 8, 16, 24, 32, and 40. Blood sampling and measurement of the CL and dominant follicle were done every 8 h beginning 14 days postovulation in each group. Blood samples for detection of pulses of PRL and pulses of PGFM were obtained every hour for 24 h beginning at Hour 0. Pulse concentrations of both PGFM and PRL were lower in the FM group than in the vehicle group. Concentration of PRL was greatest at the peak of a PGFM pulse. Neither CL area (cm2) nor P4 concentration differed between groups during Hours 0 to 48 (postluteolysis). Ovulation occurred in nine of nine heifers in the vehicle group and in three of 10 heifers in the FM group. The anovulatory follicles in the FM group grew to 36.2 ± 2.9 mm, and the wall became thickened from apparent luteinization. The hypothesis that PGF2&#945; was involved in the continued P4 decrease and structural CL regression during postluteolysis was not supported. The hypotheses that pulses of PGFM and PRL were temporally related and that systemic FM treatment induced an anovulatory follicle were supported.